Continuing effort has been directed toward the development of more satisfactory means for inventory control and supermarket checkout procedures. These efforts have resulted in a Universal Product Code (UPC), presented as an array of bars and spaces. Codes of this type are readable by a diffuse reflectance scanning means.
Despite the overall workability of this system, difficulty has been encountered in the development of a satisfactory means for applying the coded message. Traditional graphic art printing techniques, using two inks for the bars and the spaces, respectively, are limited by the tendency of the ink to spread during application. Moreover, the UPC system has minimum contrast requirements between the bar code and the background, since the coded information is read by detecting diffusely scattered light as reflected by the bars and the background. Accordingly, a continuing need exists for a reliable system for applying UPC codes efficiently and accurately to a wide variety of substrates.